1. Field of the Invention
The present invention relates to a support structure for movably operating a swash plate with reduced frictional resistance in a variable displacement type hydraulic system.
2. Description of the Related Art
A support structure for a sliding portion of a swash plate in a variable displacement type hydraulic system has been described in, for example, Japanese Utility Model Publication Gazette No. 61-28062. In this publication, a variable displacement type axial piston machine is constructed so that a convex surface is formed at the rear surface of a swash plate, a concave surface is formed at an inner wall of a housing opposite to the swash plate, and thrust metal of a substantially U-shape is fixed to the concave surface, so that the rear surface of the swash plate slides along a concave guide surface of a thrust metal.
However, since the swash plate is constantly subjected to thrust from pistons, frictional resistance generated between the rear surface of the swash plate and the guide surface of the thrust metal becomes greater. Thus, the sliding resistance of the swash plate is greater, thereby requiring a greater force to operate the swash plate. Friction is an important consideration, especially in the type of structure where the swash plate is spring biased to rotatably return to the neutral position. If the sliding resistance overcomes the biasing force of the spring, the swash plate will not return to the neutral position. Also, polishing the rear surface of the plate in contact with the thrust metal will not reduce the sliding resistance.